Process for the preparing of random copolymers of conjugated dienes and vinyl aromatic hydrocarbons

ABSTRACT

A process for copolymerization of a conjugated diolefin with a vinyl aromatic hydrocarbon by a lithium type initiator in the presence of a randomizer selected from anionic surface active compounds having a hydrophilic group represented by -SO3M or OSO3M where M is Na or K, in 1 - 20 parts by weight of a hydrocarbon or halogenated hydrocarbon solvent per 1 part by weight of the monomers, which comprises initiating the polymerization reaction at 20*C. - 90*C. and polymerizing substantially all monomers at the maximum temperature below 150*C. without removal of polymerization heat.

Waited States Patent [191 Kmnatsu et al.

Yokohama, Japan [73] Assignee: Japan Synthetic Rubber Co. Ltd.,

Tokyo, Japan [22] Filed: Apr. 5, 1971 211 App]. No.: 131,508

[30] Foreign Application Priority Data Apr. 10,1970

Japan....'.; ..45/30l6l [52] US. Cl ..260/84.3, 260/83.7 [51] Int. Cl...C08f 19/06, C08f 19/08 [58] Field of Search ..260/83.7, 84.3

11] 3,734,8 8 1 May 22 1973 Primary Examiner-James A. SeidleckAttorney-Sherman and Shalloway ABSTRACT A process for copolymerizationof a conjugated diolefin with a vinyl aromatic hydrocarbon by a lithiumtype initiator in the presence of a randomizer selected from anionicsurface active compounds having a hydrophilic group represented by SO Mor OSO M where M is Na or K, in 1 20 parts by weight of a hydrocarbon orhalogenated hydrocarbon solvent per 1 part by weight of the monomers,which comprises initiating the polymerization reaction at 20C. 90C. andpolymerizing substantially all monomers at the maximum temperature below150C. without removal of polymerization heat.

11 Claims, No Drawings This invention relates to a process wherein incopolymerizing a conjugated diolefin with a vinyl aromatic hydrocarbon,the polymerization reaction is initiated by a lithium type initiator ata temperature within a specified range, followed by carrying out thereaction without removal of the polymerization heat.

Prior to the present invention in manufacturing a rubbery polymer bycopolymerizing a conjugated diolefin with a vinyl aromatic hydrocarbon,it was customary to either remove the polymerization heat or apply heatafter the initiation of the polymerization reaction so as to ensure thatthe temperature is maintained at a given level.

It has now been found that a marked reduction in the polymerization timecan be effected by not by removing the polymerization heat afterinitiation of the polymerization reaction but by utilizing thetemperature rise that results from the accumulation of the reactionheat. It has furthermore been found that by operating in this mannerrubbery polymers can be provided the physical properties of which, e.g.,cold flow, were superior to those obtained by the conventional, process(where the temperature is held constant).

According to the invention process, in polymerizing a mixture of aconjugated diolefin and a vinyl aromatic hydrocarbon in the presence ofa lithium type initiator and an adequate randomizer, the polymerizationreaction is initiated ata temperature of 20 to 90C, and thereafter thereaction is carried out without removal of the polymerization reactionheat. .In the present invention the polymerization reaction is completedin a short period of time not by removing the polymerization reactionheat after the initiation of the reaction but utilizing the temperaturerise of the reaction system that results from the accumulation of thereaction heat. As a result, rubbery polymers the molecular weightdistribution of which is extensive and accordingly which possessexcellent physical properties can be obtained.

Of the lithium type initiators which are available in I accordance withthepresent invention, typical examples include metallic lithium; alkyllithiums such as ethyl lithium, propyl lithium, n-butyl lithium,sec.-butyl lithium, tert.-butyl lithium and iso-butyl lithium; aryllithiums such-as phenyl lithium and 'tolyl lithium; alkenyl lithiumssuch as vinyl lithiumandpropenyl lithium; alkylene dilithiums such astetramethylene dilithium and hexamethylene dilithium; arylene dilithiumssuch as l,3-dilithiobenzeneand l,4-dilithiobenzene; as well asl,3,5-trilithiocyclohexane, 7 1,2,5- trilithionaphthalene,l,3,5,8tetralithiodecane and 1,2- ,3,S-tetralithio-4-hexylanthracene.

These lithium type initiatorscan be used either singly or incombinations of two tormore and can be added to the reaction system in astate of asuspension or solution in a hydrocarbon solvent.

The lithium type initiator is usually used in an amount of'0.02 2millimoles, andlpreferably 0.05 l millimole per 100 grams of themonomer. The total amount may be divided into two or more portions andbe incrementally added to the reaction system. When the reaction systemcontains some impurities, it is advantageous from the practicalstandpoint that the initiator is additionally used in sufiicient amountsto inactivate the impurities.

Examples of the conjugated diolefins which are used in the presentinvention include 1,3-butadiene, isoprene and piperylene. Examples ofthe vinyl aromatic hydrocarbons, include styrene, divinylbenzene,alphamethyl styrene, beta-methyl styrene, vinyl toluene, 1- vinylnaphthalene and 2-vinyl naphthalene, of which styrene is convenientlyused.

These conjugated diolefinsand vinyl aromatic hydrocarbons may be usedeither singly or in admixture of two or more, respectively.

A a suitable combination of a conjugated diolefin and a vinyl aromatichydrocarbon, is, for example, 1,3- butadiene and styrene, or isopreneand styrene, or 1,3-

butadiene, isoprene and styrene. As the 1,3-butadiene,

the B-B fraction obtained by cracking of naphtha in which butanes andbutenes are copresent can also be used.

The hydrocarbon solvent to be used in the present invention, include thealiphatic, alicyclic and aromatic hydrocarbons which are liquid underthe polymerization conditions. Convenient hydrocarbon solvents includesuch, as for example, n-pentane, iso-pentane, nhexane, n-heptane,n-octane, iso-octane, n-decane, cyclopentane, cyclohexane, methylcyclopentane, ethyl cyclopentane, benzene, toluene and xylene. Further,the halogenated hydrocarbons .can also be used as the solvent in theprocess of the present invention. Since the polymerization by means of alithium type initiator proceeds by an ionic mechanism, generally therate of polymerization increases with increasing polarity of thesolvent. Therefore, the polymerization reaction proceedsat a stillgreater rate by the use of a halogenated hydrocarbon solvent. Assuitable halogenated hydrocarbons, included are such as chlorobenzene,chloro- ,toluene, chloroxylene, orthodichlorobenzene, fluorobenzene,fluorotoluene, fluoroxylene and chloroethylbenzene. l

The polymerization solvent is used in an amount of 1 20 parts by weight,preferably 2 10 parts by weight, per 1 part by weight of the monomer. Ifthe'solvent is used in an amountbelow 1 part by weight per 1 part byweight of the monomers, the polymerization reaction becomes too violentand is dangerous. On the other hand, if the amount of the solventexceeds 20 parts by weight per part by weight of the monomers, theaccumulation of the polymerization heat becomes so inadequate that theadvantages of the invention cannot be attained.

The initiation of the polymerization reaction is carried out at atemperature ranging between 20 and 90C, and preferably 40 C. If thetemperature at whichthepolymerization reaction is initiated is below20C., the-initial rate of the polymerization is too low,

and thereforeit iscommercially disadvantageous. On

small. This also happens when the scale of the polymerization reactionis small. In this case the amount of heat discharged exceeds the amountof polymerization heat that is accumulated In cases such as described,it is preferred to assist the temperature rise of the polymerizationsystem by heating the system to a temperature at least 30C. higher thanthe polymerization initiation temperature.

It is preferably to carry out the polymerization reaction at atemperature below 150C. When the polymerization temperature exceeds150C, the molecular weight distribution of the resulting polymer oftenbecomes sufficient to give a disadvantageous effect on theprocessability of the product. Moreover, in the case of butadiene, whichis conventionally available in the invention, the pressure of thepolymerization system rises rapidly when the polymerization temperatureexceeds its critical temperature (152C). (Kirk-Othmer: Encyclopedia ofChemical Technology, Second Edition Vol. 3, P785 lnterscience)Therefore, the polymerization temperature below 150C is favorable fromthe standpoint of both safety and economy.

Only by appropriately selecting both the initial polymerizationtemperature and monomer concentration, is it possible to maintain themaximum polymerization temperature below 150C without removal ofpolymerization heat.

No particular restriction is imposed on the pressure of the reactionsystem as long as it is sufficient to maintain the reaction mixture inthe liquid phase. Usual pressure is 1 kg/cm.

In order to randomly copolymerize a conjugated diolefin with a vinylaromatic hydrocarbon, some randomizers should be used in addition to thelithium type initiator. Generally, the use of randomizer often decreasesthe l,4-cis and trans configurations of the diolefin units in thecopolymer. However, there are some randomizers having no tendency todecrease the 1,4-cis and trans configurations, for example, anionicsurface active compounds having a hydrophillic group represented by SO Mor OSO M, wherein M is Na, K etc., as disclosed in Japanese Patentapplication No. 2531 1/1967.

Representative examples shown in the Japanese Patent application are:

l. salts of alkyl-aryl sulfonic acids, such as potassium stearyl benzenesulfonate, potassium dodecyl benzene sulfonate, potassium nonyl benzenesulfonate, potassium decyl benzene sulfonate and sodium derivativesthereof,

2. salts of sulfuric acid esters of higher alcohols, such as potassiumstearyl sulfate, potassium dodecyl sulfate, potassium decyl sulfate,potassium nonyl sulfate and sodium derivatives thereof,

and

3. potassium N-methyl taurate, methylene bis (potassium naphthalenesulfonate) and sodium derivatives thereof, etc.

In the present invention, a randomizer having no effect on the contentsof the 1,4-configuration is preferably used in order to obtain excellentrubbery products.

The randomizer is used in an amount of 0.001 to 10 gram-atoms calculatedas the metal atom in the surface active compound per gram atom oflithium metal in the initiator used.

A molecular weight regulator can also be used, if desired.

Upon substantial completion of the reaction, the polymerization isterminated in the customary manner by adding a short stop agent such aswater or an alcohol, followed by the addition of a suitable amount of anantioxidant, and then the resulting polymer is isolated, washed anddried.

The process according to the invention is very economical because thepolymerization time is short. In addition, since the polymerizationtemperature in this process varies successively, the resulting polymerhas a broad molecular weight distribution. A polymer of this sort excelsin its physical properties. Prior to the present invention the molecularweignt distribution was broadened by such processes as (1) a processconsisting of mixing polymers having different molecular weights and (2)a process wherein the polymerization reaction was carried out by addingportioned amounts of a polymerization initiator incrementally. Ascompared with these methods, the process of the present invention is notonly simpler to practice but also the reaction time is shorter.

The polymer obtained by the invention process is characterized by thefollowing properties: (1) its cold flow is small; (2) the rollprocessability of the raw rubber is excellent; (3) its tensile strengthand elongation are favorable as compared with those of the polymersobtained by the conventional polymerization processes; (4) its cutgrowth is small. (5) The polymer obtained in the present invention hassubstantially the same or higher content of the 1,4-configuration in thepolydiolefin portions as compared with that of the polymer prepared bythe prior art process; (6) there is substantially no difference from thecopolymers obtained by the conventional polymerization processes withrespect to the monomeric composition of the copolymer; (7) practicallyno gel is present in the copolymer; and (8) the color of the polymerdoes not differ from that of the polymers obtained by the conventionalpolymerization processes.

The following examples are given for the purpose of illustrating theinvention. It is to be understood that these examples are not intendedto limit the invention in any manner except as it is limited in theappended claims.

Examples I II and Controls 1 II The copolymerization of 1,3-butadienewith styrene was carried out under the conditions indicated in Table 1.Controls 1 and II are experiments for purpose of comparison and are outof the scope of the present invention. The polymerization reaction wasoperated in the following manner. In a thoroughly dried polymerizationvessel, after purging with nitrogen, dried and purified solvent andmonomer were charged, followed by addition of sufficient n-butyl lithiumto inactivate the trace amounts of impurities contained in the system.Then the prescribed amounts of n-butyl lithium and randomizer wereadded, and the polymerization reaction was initiated. In the case ofControl I, heat was removed immediately after the initiation of thepolymerization reaction with ice water while in the latter stages of thereaction heating was carried out with hot water in order to maintain areaction temperature of 50C. On the other hand, no cooling or heatingwas carthe properties of the vulcanizates of the polymers, such 40 riedout at all from the outside in the case of Example I after initiation ofthe reaction at 50C. Ten minutes later a reaction temperature of 130C.was reached, and the polymerization was completed. Control IIillustrates the instance where the initiator was portioned 5 and addedincrementally. For maintaining a reaction temperature of 50C., thesystem was cooled after the first addition of the initiator and therandomizer, but when the conversion reached 20 percent, the system washeated. When the conversion reached 30 percent,

cent to maintain the temperature at 50C. In the case of Example II, thereaction was operated as in Control II up to the point where theconversion reached 30 percent, but after the second addition of theinitiator and the randomizer, the reaction was carried out with noexternally applied cooling or heating at all. Ten minutes later, thereaction temperature rose to 110C. and a conversion of 100 percent wasattained.

After having carried out the reactions for the prescribed period, thereactions of Examples I II and Controls I II were in all casesterminated by the addition of a small quantity of isopropyl alcohol tothe polymerization systems. As an antioxidant, 1.5 parts by weight of2,6-ditertiarybutyl-p-cresol per 100 parts by weight of the polymer wasadded to the polymerization solution. This was followed by the removalof the solvent with steam and thereafter drying the polymer for 30 hoursat 50C.

The properties of the polymers are shown in Table 2. When Control I iscompared with Example I, it is evident that the cold flow has beengreatly improved in the case of Example I which was carried out inaccordance. with the present invention. The roll processability of thepolymer (crude rubber) is also superior in the case of the polymerobtained in Example I. Further, when as modulus at 300 percent, tensilestrength, elongation,

tear strength at both room and elevated temperatures and out growth, arecompared, it is seen that improvements are demonstrated in practicallyall cases. In Con-' trol II the polymerization reaction was carried outby adding the initiator in portioned amounts incrementally TABLE 2Control Exam 10 Control Ex le Experiment number I p I II ampMicrostrueture of the polybutadiene portion:

Cis (percent) 38 39 39 38 Trans (pereent) 47 47 46 49 Vinyl (percent) 1514 15 13 Bonded styrene (percent). 25 25 25 25 Gel content (percent) 0 00 0 Intrinsic viscosity [1;] in

toluene at 30 C 3 1. 9 3. 1 2.6 Mooney viscosity M 50 48 52 50 Cold flow(mg/min.) 8. 0 0.2 0. 1 0.0 Roll processability of crude rubber PoorExcellent Excel- Good lent Properties of vuleanizate:

Hardness (J IS-Hs) G2 61 61 61 Modulus at 300% (kg./

cm! 75 78 72 74 Tensile strength (kg./

cm?) 200 245 255 255 Elongation (percent) 550 650 640 640 Tear strength:

20 C. (kg./cn1. '17 53 58 50 100 C. (kgJcmfl)..- 36 41 39 Cut growth(number of rotation required for the crack to grow 10 mm.) 11, 000 38,000 14, 000 19, 000

Notes.

1. Microstructure of the polybutadiene portion: calculated by the methodof D. Morero, Chim, e. Lindustria 91, 758 (1959).

2. Bonded styrene: Determined from the refractive index.

3. Mooney viscosity: Measured at 100C. with a Goodrich Mooneyviscometer.

4. Cold flow: Measured by extruding the polymer through a 54-inchorifice at a pressure of 3 .5 lb./in. and a temperature of 50C. In orderto measure at a steady state the extrusion speed was measured afterallowing the extrusion to continue for 10 minutes. The so obtained valuewas expressed in figure of milligrams per minute.

5. Roll processability of crude rubber: This was indicated by acomposite evaluation of roll banding property, luster and smoothness ofcrude rubber under the conditions of a roll temperature 80C., 6-inchrolls, rotation of 14/17 rpm, roll clearance of 2 mm and roll width of170 mm.

6. vulcanization conditions: 145C., minutes.

Compounding Ingredients in order to spread the molecular weightdistribution of 2%? the polymer. In consequence, substantially nodiffer- Rubber 100 ence is noted in the unvulcanized as well asvulcanized g f2 2: products of the polymer of Control II as comparedwith Zinc white: 3

those obtained in Example II, which was carried in accordance with theinvention process. However, Examh 1 !q'-i lh l di i ple II is superiorin that the reaction time 18 less than Vulcamwwn accelmof(cyclohexyl-benzothlazyl-sulfonamide) one-half that in Control II. S lfL TABLE 1 Rate of Amount of Amount of polymer- Final initiator usedrandomizer used ization rate of conversion polymer- F1rst Second FirstSecond at second Reaction Reaction ization Experiment addition additionaddition addition addition temperatime conversion number (mhm.) (mhm.)(mhm.) (mhm.) (percent) ture, C. (min.) (percent) Control I 0.500 0. 05060 130 97 Example I 0. 590 0. 059 50-130 10 100 Control II. 0. 055 0.470 0. 011 o. 047 30 50 205 98 Example II. 0. 055 0. 470 0.011 0. 047 3050-110 100 Notes-1. (mhm.) is millimoles per 100 grams of monomer.

2. Solvent: 400 parts by weight cyclohexane per 100 parts by weight ofmonomer. 3. Monomer: 75 parts by we1ght of 1,3-butad1eno and 25 parts byweight of styrene used. Total amount of monomer used was 500 grams.

4. Randomizer: Potassium dodccylbcnzenesulfonatc.

Examples 111 VI In a completely dried polymerization vessel (6L.), afterpurging with nitrogen, 3,150 g. of cyclohexane, 700 g. of butadiene andstyrene whose charge ratio is variable and a prescribed amount ofpotassium dodecylbenzene sulfonate were charged, followed by heating to50C. Then, in order to remove the trace amounts of impurities containedin the polymerization system, n-butyl lithium in an amount justsufficient to react with the impurities was added. Thereafter, thepolymerization was initiated by the prescribed amount of n-butyl lithiumand carried out with neither application of heat nor removal ofpolymerization heat.

After completion of the polymerization reaction, the product wasisolated, washed and dried in a similar procedure to that described inExamples I and 11.

Polymerization conditions and the physical properties of the productsare summarized in Tables 3 and 4.

TABLE 3 Example No. 111 IV V VI BD/S'l' ratio by wt. 65/35 75/25 85/1595/5 nBuLi, (mmole) 4.18 4.36 4.10 3.64 DBS-K (mmole) 0.418 0.391 0.3300.218 Polymerization Temp. (C) 50- 118 50-132 50- 130 50- 136Polymerization Time (min.) 12 8 12 12 Conversion 100 100 100 100 [17] intoluene at 30C. 1.55 1.73 1.89 2.17

" DBS-K Potassium dodecylbenzene sulfonate.

TABLE 4 Example No. 111 IV V VI ML at 100C. 46.5 56.5 42.5 46.5Microstructure of raw polymer cis 35 37 36 38 trans (96) 48 48 49 49 1,2vinyl (76) 17 15 15 13 Cold flow 1.6 0.30 0.42 0.66 Roll processabilityexcelexcelexcelexcellent lent lent lent Hardness [JIS K6301 (115)] 62 6161 61 Modulus at 300 (kg/cm) 80 75 80 76 Tensile strength (kg/cm) 250253 246 207 Elongation (56) 580 600 580 550 Tear strength g/ at roomtemp. 53 50 49 45 at 100C. 39 38 38 32 Compounding recipes andvulcanization conditions are the same as those given in Examples I and11. Examples VII and VIII To a completely dried polymerization vessel(16L), after purging with nitrogen, 8.0 kg. of cyclohexane, 0.5 kg. ofstyrene, 1.5 kg. of butadiene and a prescribed amount of potassiumdodecylbenzene sulfonate were added, followed by heating to the desiredinitiation temperature. The polymerization reaction and recovery of thepolymer were carried out by similar procedures to those described inExample 1. Evaluation of the polymer was also conducted in the samemanner as shown in Example I. Results are given in Table 5.

TABLE Example No. 1 VII VIII n-Butyl lithium (mhm) 0.590 0.820 0.850DBS-K" (mhm) 0.059 0.119 0.119 Polymerization initiation temp. (C.) 5070 90 maximum temp. (C.) 130 139 147 time (min.) 3 2 conversion 100 100100 Microstructure of raw polymer 1,4-cis (36) 39 38 36 1,4-trans (1%)47 47 47 1,2-vinyl (36) l4 15 14 [17] in toluene at 30C. 1.9 1.8 1.8 Gel(91:) 0 0 0 ML at 100C. 48 49.5 47 Cold flow (mg/min) 0.2 0.7 0.4 Rollprocessability excellent excellent excellent Hardness (HS) 61 61 61Modulus at 300 (kg/cm) 78 89 Tensile strength (kg/cm) 245 221 233Elongation 650 660 660 Tear strength (kg/cm) at room temp. 53 58 55 atC. 40 38 4l (mhm):mil1imoles per 100 grams of the monomers DBS-K:Potassium dodecylbenzene sulfonate Example 1X In a similar manner tothat described in Example I, 780 g. of butadiene and 260 g. of styrenewere copolymerized in the presence of 0.06 millimoles of potassiumdodecylbenzene sulfonate by adding 0.624 millimoles of n-butyl lithiuminitiator. As a solvent, 6,250 g. of benzene were used. Thepolymerization reaction was initiated at 50C and carried out withneither application of heating nor removal of polymerization heat. Themaximum polymerization temperature was attained to 102C. For completionof the polymerization reaction, 15 minutes were necessary. Termination,recovery of the polymer and evaluation of the product were conducted ina similar manner to that described in Example l.

The physical properties of the polymer obtained were equivalent to thoseof Example I.

We claim:

1. A process for copolymerization of a conjugated diolefin with a vinylaromatic hydrocarbon which comprises effecting the copolymerization byusing a lithium type initiator selected from metallic lithium andorganolithium compounds in the presence of a randomizer selected fromanionic surface active compounds having a hydrophilic group representedby -SO M or -OSO M where M is Na or K, selected from salts of alkyl arylsulfonic acids, salts of sulfuric acid esters of higher alcohols, saltsof N-methyl taurine and salts of methylene bis (naphthalene sulfonicacid), in l 20 parts by weight of a hydrocarbon or halogenatedhydrocarbon solvent per 1 part by weight of the monomers, initiating thepolymerization reaction at 20C. 90C. and polymerizing substantially allof the monomers at the maximum temperature below C. without removal ofpolymerization heat.

2. The process of claim 1 wherein the conjugated diolefin is selectedfrom the group consisting of 1,3- butadiene, isoprene and piperylene.

3. The process of claim 1 wherein the vinyl aromatic hydrocarbon isselected from the group consisting of styrene, divinylbenzene,alpha-methyl styrene and vinyl toluene.

4. The process of claim 1 wherein the temperature at which thepolymerization is initiated ranges from 40C. 70C.

5. The process of claim 1 wherein the solvent is selected from the groupconsisting of n-pentane, nhexane, n-heptane, iso-octane, cyclohexane,benzene, toluene, xylene, chlorobenzene and dichlorobenzene.

6. The process of claim 1 wherein the solvent is used in an amount of 210 parts by weight per 1 part by weight of the monomers.

7. The process of claim 1 wherein the randomizer is selected from thegroup consisting of potassium stearylbenzene sulfonate, potassiumdodecylbenzene sulfo- 9. The process of claim 1 wherein the lithium typenate, potassium nonylbenzene sulfonate, potassium deinitiator isselected from the group consisting of ethyl cylbenzene sulfonate,potassium stearyl sulfate, potaslithium, n-butyl lithium, sec-butyllithium, tert.-butyl sium dodecyl sulfate, potassium decyl sulfate,potaslithium, phenyl lithium, vinyl lithium, and teramethysium nonylsulfate, potassium N-methyl taurate, methy- 5 lene dilithiurn.

lene bis(potassium naphthalene sulfonate) and sodium 10. The process ofclaim 1 wherein the initiator is derivatives of the compounds mentionedabove. used in an amount of 0.02 2 millimoles per 100 grams 8. Theprocess of claim 1 wherein the randomizer is of the monomers.

used in an amount of 0.001 gram atoms calculated 1]. The process ofclaim 10 wherein the initiator is as the metal atom in the randomizerper 1 gram atom 10 used in an amount of 0.05 1 millimole per 100 gramscalculated as the lithium atom in the initiator. of the monomers.

2. The process of claim 1 wherein the conjugated diolefin is selectedfrom the group consisting of 1,3-butadiene, isoprene and piperylene. 3.The process of claim 1 wherein the vinyl aromatic hydrocarbon isselected from the group consisting of styrene, divinylbenzene,alpha-methyl styrene and vinyl toluene.
 4. The process of claim 1wherein the temperature at which the polymerization is initiated rangesfrom 40*C. - 70*C.
 5. The process of claim 1 wherein the solvent isselected from the group consisting of n-pentane, n-hexane, n-heptane,iso-octane, cyclohexane, benzene, toluene, xylene, chlorobenzene anddichlorobenzene.
 6. The process of claim 1 wherein the solvent is usedin an amount of 2 - 10 parts by weight per 1 part by weight of themonomers.
 7. The process of claim 1 wherein the randomizer is selectedfrom the group consisting of potassium stearylbenzene sulfonate,potassium dodecylbenzene sulfonate, potassium nonylbenzene sulfonate,potassium decylbenzene sulfonate, potassium stearyl sulfate, potassiumdodecyl sulfate, potassium decyl sulfate, potassium nonyl sulfate,potassium N-methyl taurate, methylene bis(potassium naphthalenesulfonate) and sodium derivatives of the compounds mentioned above. 8.The process of claim 1 wherein the randomizer is used in an amount of0.001 - 10 gram atoms calculated as the metal atom in the randomizer per1 gram atom calculated as the lithium atom in the initiator.
 9. Theprocess of claim 1 wherein the lithium type initiator is selected fromthe group consisting of ethyl lithium, n-butyl lithium, sec-butyllithium, tert.-butyl lithium, phenyl lithium, vinyl lithium, andteramethylene dilithium.
 10. The process of claim 1 wherein theinitiator is used in an amount of 0.02 - 2 millimoles per 100 grams ofthe monomers.
 11. The process of claim 10 wherein the initiator is usedin an amount of 0.05 - 1 millimole per 100 grams of the monomers.